Displacement control valve of clutchless variable displacement inclined plate-type compressor

ABSTRACT

A displacement control valve of a clutchless variable displacement inclined plate-type compressor for controlling the discharge displacement of the compressor by opening and closing a communication path between a discharge chamber and a crank chamber. The displacement control valve has a valve hole ( 106 ) formed in the communication path and always communicating with the discharge chamber, an inside control valve ( 100 ) for opening and closing the valve hole ( 106 ) by a valve body ( 112 ) operated in response to expansion and contraction of a pressure sensing member ( 109 ) for sensing a suction pressure, and an operation switching device ( 120 ) connected to the inside control valve for switching the inside control valve between an operating condition where the valve body opens and closes the valve hole in response to the expansion and contraction of the pressure sensing member and a non-operating condition where the valve body opens the valve hole independently of the expansion and contraction of the pressure sensing member. In this displacement control valve, because a discharge pressure Pd acts on both the valve body ( 112 ) and a pressure sensing rod ( 110 ), the force of the discharge pressure Pd for urging the valve body ( 112 ) in a valve opening direction is (Sr−Sv)Pd. The displacement control valve can be made smaller than conventional displacement control valves because (Sr−Sv) is very small.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a displacement control valve of aclutchless variable displacement inclined plate-type compressor which isconnected directly to a drive source without using a clutch.

BACKGROUND ART OF THE INVENTION

Patent Document 1 discloses a displacement control valve of a clutchlessvariable displacement inclined plate-type compressor for controlling adischarge displacement of the compressor by opening and closing a valvehole formed in a communication path between a discharge chamber and acrank chamber of the compressor, the displacement control valveincluding the valve hole always communicating with the crank chamber, aninside control valve for opening and closing the valve hole by a valvebody operated in response to expansion and contraction of a pressuresensing member for sensing a suction pressure, and an electromagneticsolenoid connected to the inside control valve for switching the insidecontrol valve between an operating condition where the valve body opensand closes the valve hole in response to the expansion and contractionof the pressure sensing member and a non-operating condition where thevalve body opens the valve hole independently of the expansion andcontraction of the pressure sensing member, and the displacement controlvalve controls the discharge displacement so that a suction pressure anda discharge pressure have a predetermined correlation. This PatentDocument 1 describes that the displacement control property is expressedby the following equation in a region of Pd>Pd₀.Ps=P ₀−(Pd−Pc)S ₁ /S ₂Where,

-   Pd: discharge pressure-   Pc: crank chamber pressure-   Ps: suction chamber-   P₀: equivalent internal pressure of bellows-   S¹: cross-sectional area of valve hole-   S₂: effective cross-sectional area of bellows-   Patent Document 1: JP-A-7-127566

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, there are the following problems in the displacement controlvalve disclosed in the above-described Patent Document 1.

Because the discharge pressure Pd urges the valve body in a direction ofvalve closing, in order to forcibly open the valve body by degaussing ofthe electromagnetic solenoid, it is necessary to set the force of areleasing spring of the electromagnetic solenoid at a value of (Pd-31Ps)S₁ or more. In order to forcibly open the valve body in a region witha high discharge pressure Pd, it is necessary to use a releasing springwith a great spring force, and it is necessary to generate a greatelectromagnetic force for exciting the electromagnetic solenoid andattracting a movable core against the spring force of the releasingspring, and whereby, the electromagnetic solenoid becomes large.

Accordingly, paying attention to the above-described problems, an objectof the present invention is to provide a displacement control valve of aclutchless variable displacement inclined plate-type compressor, whichcan be made smaller than the displacement control valve disclosed inPatent Document 1.

Means for Solving the Problems

To achieve the above-described object, a displacement control valve of aclutchless variable displacement inclined plate-type compressoraccording to the present invention is provided as a displacement controlvalve for controlling a discharge displacement of the compressor byopening and closing a communication path between a discharge chamber anda crank chamber of the compressor. The displacement control valvecomprises a valve hole formed in the communication path and alwayscommunicating with the discharge chamber, an inside control valve foropening and closing the valve hole by a valve body operated in responseto expansion and contraction of a pressure sensing member for sensing asuction pressure, and an operation switching device connected to theinside control valve for switching the inside control valve between anoperating condition where the valve body opens and closes the valve holein response to the expansion and contraction of the pressure sensingmember and a non-operating condition where the valve body opens thevalve hole independently of the expansion and contraction of thepressure sensing member.

In the present invention, because the valve hole is always communicatedwith the discharge chamber, the force for urging the valve body in avalve opening direction by a discharge pressure Pd can be decreased ascompared with that in the displacement control valve disclosed in theaforementioned Patent Document 1, and the switching device for forciblyopening the valve body may be made smaller.

In such a displacement control valve according to the present invention,a structure is preferably employed wherein the above-described operationswitching device has an electromagnetic solenoid, when theelectromagnetic solenoid is excited, the inside control valve becomesthe operating condition, and when the electromagnetic solenoid isdegaussed, the inside control valve becomes the non-operating condition.In such a structure, because the variable displacement inclinedplate-type compressor can be switched to between a displacement controlcondition and a minimum displacement condition by exciting/degaussingthe electromagnetic solenoid, the control unit for the variabledisplacement inclined plate-type compressor may be simplified.

Further, in the displacement control valve according to the presentinvention, it is preferred that the electromagnetic solenoid includes amovable core connected to the inside control valve and a positioningmember for positioning the inside control valve at an operating positionwhen the electromagnetic solenoid is excited. By providing such apositioning member, it becomes possible to position the inside controlvalve at an operating position by exciting the electromagnetic solenoid,and the switching of the variable displacement inclined plate-typecompressor to its operating condition becomes possible by the excitationof the electromagnetic solenoid.

Further, in the displacement control valve according to the presentinvention, it is preferred that the positioning member is formed by oneend of the pressure sensing member and an end surface of a case of theelectromagnetic solenoid. By forming the positioning member with one endof the pressure sensing member and the case of the electromagneticsolenoid, it is not necessary to dispose a particular positioning memberseparately, and the structure of the displacement control valve may besimplified.

Further, in the displacement control valve according to the presentinvention, it is preferred that the electromagnetic solenoid includes areleasing spring for urging a movable core in a direction apart from afixed core, and when the electromagnetic solenoid is degaussed, theinside control valve becomes the non-operating condition by thereleasing spring. Because the releasing spring of the electromagneticsolenoid can turn the inside control valve into the non-operatingcondition, it is not necessary to provide a spring separately forturning the inside control valve into the non-operating condition, andthe structure of the displacement control valve may be simplified.

Further, in a preferred embodiment of the present invention, the insidecontrol valve includes a pressure sensing rod which is slidably insertedinto a hole formed in a valve housing and communicating with the valvehole and which is connected to the valve body, and a cross-sectionalarea of the pressure sensing rod is set greater than a cross-sectionalarea of the valve hole. In such a structure, because a control propertyis realized wherein the suction pressure decreases when the dischargepressure increases, the discharge displacement increases in a highthermal-load region with a high discharge pressure. Therefore, a coolercomprising a variable displacement inclined plate-type compressor withthis displacement control valve does not deteriorate in coolingperformance even in a high thermal-load region with a high dischargepressure.

Alternatively, in another preferred embodiment of the present invention,the inside control valve includes a pressure sensing rod which isslidably inserted into a hole formed in a valve housing andcommunicating with the valve hole and which is connected to the valvebody, and a cross-sectional area of the pressure sensing rod is setsmaller than a cross-sectional area of the valve hole. In such astructure, because a control property is realized wherein the suctionpressure increases when the discharge pressure increases, the dischargedisplacement decreases in a region of a high discharge pressure. As aresult, occurrence of a condition, in which the compressor operates atan excessive load, may be prevented.

Effect According to the Invention

In the displacement control valve of a clutchless variable displacementinclined plate-type compressor according to the present invention,because the valve hole is always communicated with the dischargechamber, the force for urging the valve body in a valve openingdirection by a discharge pressure can be decreased as compared with thatin the displacement control valve disclosed in the aforementioned PatentDocument 1, and the switching device for forcibly opening the valve bodymay be made smaller than that in the displacement control valve ofPatent Document 1. Therefore, the displacement control valve of aclutchless variable displacement inclined plate-type compressoraccording to the present invention can be made smaller than thedisplacement control valve of Patent Document 1.

Brief Explanation of the Drawings

FIG. 1 is a vertical sectional view of a clutchless variabledisplacement inclined plate-type compressor having a displacementcontrol valve according to an embodiment of the present invention.

FIGS. 2A and 2B are sectional views of the displacement control valveaccording to the embodiment of the present invention, showing operationsof an inside control valve when an electromagnetic solenoid is excited,FIG. 2C is a sectional view of the displacement control valve, showingan operation of the inside control valve when the electromagneticsolenoid is degaussed, and FIG. 2D is an enlarged, partial sectionalview of the inside control valve.

FIGS. 3A and 3B are graphs showing the control property of thedisplacement control valve according to the embodiment of the presentinvention, FIG. 3A shows a control property in a case of Sr>Sv, and FIG.3B shows a control property in a case of Sr<Sv.

EXPLANATION OF SYMBOLS

-   1: clutchless variable displacement inclined plate-type compressor-   2: displacement control valve-   17: crank chamber-   21: suction chamber-   22: discharge chamber-   26: concave portion-   100: inside control valve-   101: valve housing-   102: pressure sensing chamber-   103: valve chamber-   106: valve hole-   109: bellows assembly-   110: pressure sensing rod-   112: valve body-   120: electromagnetic solenoid

THE BEST MODE FOR CARRYING OUT THE INVENTIOn

Hereinafter, desirable embodiments of a displacement control valve of aclutchless variable displacement inclined plate-type compressoraccording to the present invention will be explained referring tofigures.

FIGS. 1 and 2 depict a variable displacement inclined plate-typecompressor having a displacement control valve according to anembodiment of the present invention. As depicted in FIG. 1, a variabledisplacement inclined plate-type compressor 1 has a main shaft 10, arotor 11 fixed to main shaft 10, and an inclined plate 12 supported bymain shaft 10 at a condition capable of changing its inclination angle.Inclined plate 12 is connected to rotor 11 via a link mechanism 13allowing the change of the inclination angle of inclined plate 12, androtates synchronously with rotor 11 and main shaft 10. Piston 15 isengaged with inclined plate 12 via a pair of shoes 14 sliding on theperiphery of inclined plate 12. Piston 15 is inserted into a cylinderbore 16a formed in a cylinder block 16. A plurality of pistons 15 aredisposed around main shaft 10 at an interval with each other in thecircumferential direction.

A crank chamber 17 containing main shaft 10, rotor 11 and inclined plate12 is formed by cylinder block 16 and a dish-like front housing 18. Mainshaft 10 extends to outside through front housing 18. A shaft sealmember 19 is disposed for sealing the through portion of main shaft 10in front housing 18. A pulley 20 is fixed at a tip portion of main shaft10. In a case where variable displacement inclined plate-type compressor1 is a compressor used for a refrigeration cycle of an air conditioningsystem for vehicles, pulley 20 is connected, for example, to an engineof a vehicle (not shown) via a belt (not shown).

A cylinder head 23 forming a suction chamber 21 and a discharge chamber22 is disposed at a position on a side of cylinder block 16 opposite tothe side of front housing 18. Suction chamber 21 is connected to anevaporator (not shown), which is provided in an external circuit, forexample, a refrigeration cycle of an air conditioning system forvehicles, via a suction port (not shown). Discharge chamber 22 isconnected to a condenser (not shown), which is provided in an externalcircuit, for example, a refrigeration cycle of an air conditioningsystem for vehicles, via a discharge port (not shown).

A valve plate 24 formed with suction hole 21 a and discharge hole 22 acommunicating with cylinder bore 16a is provided between cylinder block16 and cylinder head 23. A discharge valve and a suction valve (notshown) are attached to the valve plate 24. Crank chamber 17 and suctionchamber 21 are communicated with each other via an orifice hole 24 aformed on valve plate 24.

Front housing 18, cylinder block 16, valve plate 24 and cylinder head 23are integrally fastened by a plurality of through bolts 25 disposed atintervals along the circumference with a center of main shaft 10.

A displacement control valve 2 for controlling the dischargedisplacement of variable displacement inclined plate-type compressor 1is fitted into and fixed in a concave portion 26 which is formed incylinder head 23 at a position adjacent to discharge chamber 22. Asshown in FIGS. 1 and 2, displacement control valve 2 has an insidecontrol valve 100 and an electromagnetic solenoid 120.

Inside control valve 100 has a cylindrical valve housing 101. Threeclosed spaces 27 a, 27 b and 27 c are defined around valve housing 101by two O-rings 101 a and 101 b tightly fitted onto the periphery ofvalve housing 101 and one O-ring 121 a tightly fitted onto the peripheryof a case 121 of electromagnetic solenoid 120.

In valve housing 101, a lateral partition wall 104 is formed fordividing the inside space of valve housing 101 into a pressure sensingchamber 102 on one end side and a valve chamber 103 on the other endside. On lateral partition wall 104, a rod insertion hole 105communicating with pressure sensing chamber 102 and a valve hole 106communicating with valve chamber 103 are formed. Rod insertion hole 105and valve hole 106 are disposed on the same axis and communicated witheach other. A communication hole 107 extending in the radial directionthrough lateral partition wall 104 is formed in lateral partition wall104 passing through the communicating portion between rod insertion hole105 and valve hole 106.

Pressure sensing chamber 102 communicates with suction chamber 21 via acommunication hole 108 formed on the circumferential wall of valvehousing 101, closed space 27 c and a communication path 23 a formed incylinder head 23. Communication hole 107 communicates with dischargechamber 22 via closed space 27 b and a communication path 23 b formed incylinder head 23. Valve hole 106 communicating with communication hole107 always communicates with discharge chamber 22. Valve chamber 103communicates with crank chamber 17 via closed space 27 a, acommunication path 23 c formed in cylinder head 23 and communicationpath 16b formed in cylinder block 16.

A bellows assembly 109 functioning a pressure sensing member, in which aspring is disposed at a vacuum inside condition, is disposed in pressuresensing chamber 102. One end of a pressure sensing rod 110 is connectedto one end 109 a of bellows assembly 109, and the other end of pressuresensing rod 110 is slidably inserted into rod insertion hole 105. Asmall-diameter rod 111 extending from the other end of pressure sensingrod 110 is inserted into valve hole 106 at a movable condition with agap. A spring 113 for urging a valve body 112 in a direction approachingvalve hole 106 is disposed in valve chamber 103. Inside control valve100 is formed by a series of structures from valve housing 101 to spring113.

The end portion of pressure sensing chamber 102 side of valve housing101 of inside control valve 100 is press fitted into one end of case 121of electromagnetic solenoid 120. As aforementioned, O-ring 121 a forforming closed space 27 c is fitted onto the periphery of the one endportion of case 121.

Electromagnetic solenoid 120 has a fixed core 122 disposed in case 121,a movable core 123 disposed facing its one end to one end of fixed core122, a releasing spring 124 for urging movable core 123 in a directionapart from the fixed core, and an electromagnetic coil 125 surroundingfixed core 122 and movable core 123. The space for containing movablecore 123 is communicated with pressure sensing chamber 102, and is in acondition of the same pressure as that in pressure sensing chamber 102.The other end 109 a of bellows assembly 109 is connected to the otherend of movable core 123. The other end 109 a is disposed so as to beable to engage with an end surface inner edge 121 a near theabove-described one end of case 121 of electromagnetic solenoid 120.

Next, the operation of displacement control valve 2 will be explained.

In a case where clutchless variable displacement inclined plate-typecompressor 1 is operated at a displacement control condition, as shownin FIGS. 2A and 2B, movable core 123 is moved toward fixed core 122against the urging force of releasing spring 124 by excitingelectromagnetic coil 125, and bellows assembly 109, ultimately, insidecontrol valve 100, is positioned at its operating position by bringingthe other end 109 b of bellows assembly 109 into contact with endsurface inner edge 121 b of case 121 of electromagnetic solenoid 120.Inside control valve 100 becomes its operating condition, in which valvebody 112 opens and closes valve hole 106, in response to the expansionand contraction of bellows assembly 109 which is a pressure sensingmember4.

When inside control valve 100 is in the operating condition, if thesuction pressure is lower than a set value, as shown in FIG. 2B, bellowsassembly 109 expands, and valve body 112 connected to bellows assembly109 via pressure sensing rod 110 and small-diameter rod 111 opens valvehole 106 in response to the expansion of bellows assembly 109.High-pressure refrigerant gas is supplied from discharge chamber 22 tocrank chamber 17 through communication hole 23 b, communication hole107, valve hole 106, valve chamber 103, closed space 27 a, communicationpath 23 c and communication path 16 b. The crank chamber pressureincreases, the inclination angle of the inclined plate decreases, thedischarge displacement of variable displacement inclined plate-typecompressor 1 decreases, and the suction pressure gradually increases.

If the suction pressure exceed the set value, as shown in FIG. 2A,bellows assembly 109 contracts, and valve body 112 connected to bellowsassembly 109 via pressure sensing rod 110 and small-diameter rod 111closes valve hole 106 in response to the contraction of bellows assembly109. By this, the supply of high-pressure refrigerant gas from dischargechamber 22 to crank chamber 17 is stopped. Since orifice path 24 a hasan area enough to exhaust blow-by gas, which leaks from cylinder bore16a to crank chamber 17 when piston 15 compresses refrigerant gas incylinder bore 16 a, into suction chamber 21, the crank chamber pressuregradually decreases. When the crank chamber pressure decreases, theinclination angle of the inclined plate increases, the dischargedisplacement of variable displacement inclined plate-type compressor 1increases, and the suction pressure gradually decreases.

Thus, by the operation of inside control valve 100, the opening/closingof valve hole 106 is repeated so that the suction pressure becomes theset value, and the discharge displacement of variable displacementinclined plate-type compressor 1 is variably controlled.

When electromagnetic coil 125 is degaussed, as shown in FIG. 2C, theother end 109 b of bellows assembly 109 moves away from end surfaceinner edge 121 b of case 120 of electromagnetic solenoid 120 byreceiving the urging force of releasing spring 124, bellows assembly 109is positioned at the non-operating position, and inside control valve100 is positioned at its non-operating position. By this, inside controlvalve 100 is kept at the non-operating condition, where valve body 112opens valve hole 106, independently from the expansion and contractionof bellows assembly 109 which is a pressure sensing member. The liftingamount of valve body 112 is regulated by the contact of the end 109 a ofbellows assembly 109 with lateral partition wall 104. In this state,high-pressure refrigerant gas is supplied from discharge chamber 22 tocrank chamber 17, the crank chamber pressure increases, the inclinationangle of the inclined plate decreases down to the minimum inclinationangle, the discharge displacement of variable displacement inclinedplate-type compressor 1 is decreased down to the minimum displacement,and it is maintained at the minimum displacement. Because the dischargedisplacement of variable displacement inclined plate-type compressor 1can be minimized by the degaussing of electromagnetic coil 125,displacement control valve 2 can be used for a clutchless variabledisplacement inclined plate-type compressor directly connected to anexternal drive source without using a clutch.

The control property of displacement control valve 2 is represented bythe following equation (1).Ps=−(Sr−Sv)Pd/{Sb−(Sr−Sv)}+(f+αSv−F)/{Sb−(Sr−Sv)}  (1)Where,

-   Pd: discharge pressure-   α: pressure difference between crank chamber and suction chamber-   F: urging force of bellows assembly incorporating a spring-   f: urging force of spring 113-   Sb: effective cross-sectional area of bellows assembly 109-   Sv: cross-sectional area of valve hole 106-   Sr: cross-sectional area of pressure sensing rod 110

In displacement control valve 2, because discharge pressure Pd acts onboth valve body 112 and pressure sensing rod 110, the force of dischargepressure Pd for urging valve body 112 in the valve closing direction is(Sr−Sv)Pd. Because (Sr−Sv) is very small, the (Sr−Sv)Pd is much smallerthan PdSv in the aforementioned Patent Document 1. Therefore,displacement control valve 2 can be made smaller that the displacementcontrol valve of Patent Document 1.

In the displacement control valve of the aforementioned Patent Document1, because the gradient of the correlation line of Ps relative to Pd is−-S₁/S₂, the gradient cannot be changed unless a cross-sectional area S₁of a valve hole or an effective cross-sectional area S₂ of a bellows,which are base specifications of a displacement control valve, ischanged. Namely, the property of the displacement control cannot beeasily changed. On the other hand, in displacement control valve 2,because the gradient of the correlation line of Ps relative to Pd is−(Sr−Sv)/{Sb−(Sr−Sv)}, if the sectional area Sr ofthe pressure sensingrod is changed, even if the cross-sectional area Sv of the valve holeand the effective cross-sectional area Sb of the bellows assembly, whichare base specifications of displacement control valve 2, are notchanged, the gradient can be changed. Therefore, the property of thedisplacement control can be easily changed.

Further, in the displacement control valve of the aforementioned PatentDocument 1, if it is tried to make the displacement control valvesmaller without changing the gradient of the correlation line of Psrelative to Pd, ultimately, without changing the property of thedisplacement control, it is necessary to make SI and S₂ smallersimultaneously. If a cross-sectional area S₁ of a valve hole is madesmaller, the velocity of high-pressure refrigerant gas, flowing into acrank chamber through a valve hole after a valve body is forciblyopened, decreases, the time required for changing the displacement ofthe inclined plate-type compressor to the minimum displacementincreases, and the property of the displacement control deteriorates.Therefore, it is difficult to make it smaller. On the other hand, indisplacement control valve 2, because the gradient of the correlationline of Ps relative to Pd is −(Sr−Sv)/{Sb−(Sr−Sv)}, the effectivecross-sectional area Sb of the bellows can be made smaller by changingthe cross-sectional area Sr of pressure sensing rod 110 without changingthe cross-sectional area Sv of valve hole 106. Therefore, it is easy tomake it smaller.

Because displacement control valve 2 can switch clutchless variabledisplacement inclined plate-type compressor 1 between a displacementcontrol condition and a minimum displacement condition byexcitation/degaussing of electromagnetic solenoid 120, by using thisdisplacement control valve 2, the control unit for variable displacementinclined plate-type compressor 1 may be simplified.

Further, in displacement control valve 2, because provided is thepositioning member formed by the other end 109 b of bellows assembly 109and the end surface inner edge 121 b of case 121 of electromagneticsolenoid 120, it is possible to position inside control valve 100 at itsoperating position by the excitation of electromagnetic solenoid 120,and it is possible to switch variable displacement inclined plate-typecompressor 1 to the displacement control condition by the excitation ofelectromagnetic solenoid 120. In displacement control valve 2, becausethe positioning member is formed by the other end 109 b of bellowsassembly 109 and the end surface inner edge 121 b of case 121 ofelectromagnetic solenoid 120, it is not necessary to provide aparticular positioning member separately, and the valve structure issimplified.

Further, in displacement control valve 2, because releasing spring 124of electromagnetic solenoid 120 turns inside control valve 100 to thenon-operating condition, it is not necessary to provide a spring forturning inside control valve 100 to the non-operating conditionseparately, and the valve structure is simplified.

In displacement control valve 2, when the cross-sectional area Sr ofpressure sensing rod 110 is set greater than the cross-sectional area Svof the valve hole. as shown in FIG. 3A, because the control property isrealized wherein the suction pressure Ps decreases when the dischargepressure Pd increases, the discharge displacement of variabledisplacement inclined plate-type compressor 1 increases in a highthermal-load region with a high discharge pressure. Therefore, a coolercomprising variable displacement inclined plate-type compressor 1 withdisplacement control valve 2 does not deteriorate in cooling performanceeven in a high thermal-load region with a high discharge pressure.

On the other hand, when the cross-sectional area Sr of pressure sensingrod 110 is set smaller than the cross-sectional area Sv of the valvehole. as shown in FIG. 3B, because the control property is realizedwherein the suction pressure Ps increases when the discharge pressure Pdincreases, the discharge displacement of variable displacement inclinedplate-type compressor 1 decreases in a region of a high dischargepressure. As a result, occurrence of a condition, in which variabledisplacement inclined plate-type compressor 1 operates at an excessiveload and it may be damaged, may be prevented.

In the above-described embodiment, although the positioning member isformed by the other end 109 b of bellows assembly 109 and the endsurface inner edge 121 b of case 121 of electromagnetic solenoid 120,the positioning member may be formed by the attractive portions ofmovable core 123 and fixed core 122. Moreover, an adjusting member foradjusting the urging force of spring 113 from outside may be provided.

INDUSTRIAL APPLICATIONS OF THE INVENTION

The present invention can be applied broadly for displacement controlvalves of clutchless variable displacement inclined plate-typecompressors. In particular, it is suitable as a displacement controlvalve for a compressor provided in a refrigeration cycle of an airconditioning system for vehicles.

1. A displacement control valve of a clutchless variable displacementinclined plate-type compressor for controlling a discharge displacementof said compressor by opening and closing a communication path between adischarge chamber and a crank chamber of said compressor, saiddisplacement control valve comprising: a valve hole formed in saidcommunication path and communicating with said discharge chamber; aninside control valve for opening and closing said valve hole by a valvebody operated in response to expansion and contraction of a pressuresensing member for sensing a suction pressure; and an operationswitching device connected to said inside control valve for switchingsaid inside control valve between an operating condition where saidvalve body opens and closes said valve hole in response to saidexpansion and contraction of said pressure sensing member and anon-operating condition where said valve body opens said valve holeindependently of said expansion and contraction of said pressure sensingmember.
 2. The displacement control valve of a clutchless variabledisplacement inclined plate-type compressor according to claim 1,wherein said operation switching device has an electromagnetic solenoid,when said electromagnetic solenoid is excited, said inside control valveswitches to said operating condition, and when said electromagneticsolenoid is degaussed, said inside control valve switches to saidnon-operating condition.
 3. The displacement control valve of aclutchless variable displacement inclined plate-type compressoraccording to claim 2, wherein said electromagnetic solenoid includes amovable core connected to said inside control valve and a positioningmember for positioning said inside control valve at an operatingposition when said electromagnetic solenoid is excited.
 4. Thedisplacement control valve of a clutchless variable displacementinclined plate-type compressor according to claim 3, wherein saidpositioning member is formed by one end of said pressure sensing memberand an end surface of a case of said electromagnetic solenoid.
 5. Thedisplacement control valve of a clutchless variable displacementinclined plate-type compressor according to claim 2, wherein saidelectromagnetic solenoid includes a releasing spring for urging amovable core in a direction apart from a fixed core, and when saidelectromagnetic solenoid is degaussed, said inside control valveswitches to said non-operating condition by said releasing spring. 6.The displacement control valve of a clutchless variable displacementinclined plate-type compressor according to claim 1, wherein said insidecontrol valve includes a pressure sensing rod which is slidably insertedinto a hole formed in a valve housing and communicating with said valvehole and which is connected to said valve body, and a cross-sectionalarea of said pressure sensing rod is greater than a cross-sectional areaof said valve hole.
 7. The displacement control valve of a clutchlessvariable displacement inclined plate-type compressor according to claim1, wherein said inside control valve includes a pressure sensing rodwhich is slidably inserted into a hole formed in a valve housing andcommunicating with said valve hole and which is connected to said valvebody, and a cross-sectional area of said pressure sensing rod is smallerthan a cross-sectional area of said valve hole.
 8. The displacementcontrol valve of a clutchless variable displacement inclined plate-typecompressor according to claim 3, wherein said electromagnetic solenoidincludes a releasing spring for urging a movable core in a directionapart from a fixed core, and when said electromagnetic solenoid isdegaussed, said inside control valve switches to said non-operatingcondition by said releasing spring.
 9. The displacement control valve ofa clutchless variable displacement inclined plate-type compressoraccording to claim 4, wherein said electromagnetic solenoid includes areleasing spring for urging a movable core in a direction apart from afixed core, and when said electromagnetic solenoid is degaussed, saidinside control valve switches to said non-operating condition by saidreleasing spring.
 10. The displacement control valve of a clutchlessvariable displacement inclined plate-type compressor according to claim2, wherein said inside control valve includes a pressure sensing rodwhich is slidably inserted into a hole formed in a valve housing andcommunicating with said valve hole and which is connected to said valvebody, and a cross-sectional area of said pressure sensing rod is greaterthan a cross-sectional area of said valve hole.
 11. The displacementcontrol valve of a clutchless variable displacement inclined plate-typecompressor according to claim 3, wherein said inside control valveincludes a pressure sensing rod which is slidably inserted into a holeformed in a valve housing and communicating with said valve hole andwhich is connected to said valve body, and a cross-sectional area ofsaid pressure sensing rod is greater than a cross-sectional area of saidvalve hole.
 12. The displacement control valve of a clutchless variabledisplacement inclined plate-type compressor according to claim 4,wherein said inside control valve includes a pressure sensing rod whichis slidably inserted into a hole formed in a valve housing andcommunicating with said valve hole and which is connected to said valvebody, and a cross-sectional area of said pressure sensing rod is greaterthan a cross-sectional area of said valve hole.
 13. The displacementcontrol valve of a clutchless variable displacement inclined plate-typecompressor according to claim 5, wherein said inside control valveincludes a pressure sensing rod which is slidably inserted into a holeformed in a valve housing and communicating with said valve hole andwhich is connected to said valve body, and a cross-sectional area ofsaid pressure sensing rod is greater than a cross-sectional area of saidvalve hole.
 14. The displacement control valve of a clutchless variabledisplacement inclined plate-type compressor according to claim 8,wherein said inside control valve includes a pressure sensing rod whichis slidably inserted into a hole formed in a valve housing andcommunicating with said valve hole and which is connected to said valvebody, and a cross-sectional area of said pressure sensing rod is greaterthan a cross-sectional area of said valve hole.
 15. The displacementcontrol valve of a clutchless variable displacement inclined plate-typecompressor according to claim 9, wherein said inside control valveincludes a pressure sensing rod which is slidably inserted into a holeformed in a valve housing and communicating with said valve hole andwhich is connected to said valve body, and a cross-sectional area ofsaid pressure sensing rod is greater than a cross-sectional area of saidvalve hole.
 16. The displacement control valve of a clutchless variabledisplacement inclined plate-type compressor according to claim 2,wherein said inside control valve includes a pressure sensing rod whichis slidably inserted into a hole formed in a valve housing andcommunicating with said valve hole and which is connected to said valvebody, and a cross-sectional area of said pressure sensing rod is smallerthan a cross-sectional area of said valve hole.
 17. The displacementcontrol valve of a clutchless variable displacement inclined plate-typecompressor according to claim 3, wherein said inside control valveincludes a pressure sensing rod which is slidably inserted into a holeformed in a valve housing and communicating with said valve hole andwhich is connected to said valve body, and a cross-sectional area ofsaid pressure sensing rod is smaller than a cross-sectional area of saidvalve hole.
 18. The displacement control valve of a clutchless variabledisplacement inclined plate-type compressor according to claim 4,wherein said inside control valve includes a pressure sensing rod whichis slidably inserted into a hole formed in a valve housing andcommunicating with said valve hole and which is connected to said valvebody, and a cross-sectional area of said pressure sensing rod is smallerthan a cross-sectional area of said valve hole.
 19. The displacementcontrol valve of a clutchless variable displacement inclined plate-typecompressor according to claim 5, wherein said inside control valveincludes a pressure sensing rod which is slidably inserted into a holeformed in a valve housing and communicating with said valve hole andwhich is connected to said valve body, and a cross-sectional area ofsaid pressure sensing rod is smaller than a cross-sectional area of saidvalve hole.
 20. The displacement control valve of a clutchless variabledisplacement inclined plate-type compressor according to claim 8,wherein said inside control valve includes a pressure sensing rod whichis slidably inserted into a hole formed in a valve housing andcommunicating with said valve hole and which is connected to said valvebody, and a cross-sectional area of said pressure sensing rod is smallerthan a cross-sectional area of said valve hole.
 21. The displacementcontrol valve of a clutchless variable displacement inclined plate-typecompressor according to claim 9, wherein said inside control valveincludes a pressure sensing rod which is slidably inserted into a holeformed in a valve housing and communicating with said valve hole andwhich is connected to said valve body, and a cross-sectional area ofsaid pressure sensing rod is smaller than a cross-sectional area of saidvalve hole.